Some pressure vessels, including munitions, may be inherently dangerous. Due to those potential inherent dangers, and the grave effects an accident or unplanned incident involving munitions can have, the U.S. Government has promulgated insensitive munitions standards (“IM Standards”) to ensure that munitions operate safely and predictably. These standards require munitions—ammunition, rockets, missiles, explosives, or their shipping containers—to reliably fulfill performance, readiness, and operational requirements on demand, while minimizing the hazards of inadvertent initiation triggered by excessive temperature. Rockets are an example of munitions that must comply with U.S. Government IM standards.
A rocket motor is a pressure vessel that is propelled by a rearward discharge of gas generated by the combustion of propellant inside the motor. A rocket motor typically includes a casing or motor tube, frequently called a combustion chamber, partially filled with combustible material, and an exhaust nozzle. The combustible material at fuels the rocket is typically a single liquid or solid propellant, but can a combination of combustible materials and oxidizers.
When designed to comply with IM standards, rockets are expected to (1) enhance survivability by reducing the potential for collateral damage to logistic and tactical combat systems, (2) minimize accidental personnel injury, and (3) provide for more cost effective and efficient transport, storage and handling. IM standards set forth tests and test procedures to assess the safety and characteristics for all non-nuclear munitions, munitions subsystems, and explosive devices, including rockets.
Until now, efforts to design rockets that satisfy IM standards have had limited success. Some attempts involved designing a rocket motor that includes an insensitive munitions charge. For example, Solberg et al. in U.S. Pat. No. 6,619,029 disclose an insensitive munitions charge located inside of the motor casing to auto-ignite and release gas at a temperature below the primary propellant grain auto-ignition temperature. Other attempts have involved an ordnance venting system. For example, Kim et al. in U.S. Pat. No. 6,363,855 disclose a deflagrating composition with a high energy material that detonates during cook-off to rupture the ordnance housing to relieve pressure. Still other attempts have involved a thermoplastic warhead adapter. For example, Kim et al. in U.S. Pat. No. 6,338,242 disclose a thermoplastic adapter that is fitted over a dome plug located in a vent hole of the motor casing that melts away at elevated temperatures to relieve pressure.
While these and other efforts to design munitions and rockets that satisfy mandated IM standards have been made, those efforts have not created munitions that fully satisfy the need for both reliable operation and cost effective production. There remains a need to provide munitions with improved features that potentially enhance safety or that reliably meet IM standards.